Portable electronic devices, such as mobile telephones, personal digital assistants, laptop computers, tablet computers, global positioning system receivers, portable games, radios, cameras and camera accessories, and the like are becoming increasingly widely used globally in many different environments. It is often important that the housings of such devices be made from materials that are able to withstand the rigors of frequent use and can meet challenging aesthetic demands while not interfering with their intended operability. It is often desirable that such materials have good stiffness and impact resistance and that they exhibit minimal shrinkage (i.e., low warpage or high dimensional stability) when they are formed (as by injection molding, for example) into housings.
Thermoplastic polyamide compositions are desirable for use in making housings for portable electronic devices because of their good physical properties and that they may be conveniently and flexibly molded into a variety of articles of varying degrees of complexity and intricacy. Reinforcing agents are typically added to polyamide compositions to increase stiffness, but can often result in compositions that exhibit undesirable degrees of anisotropic shrinkage up on molding. It would thus be desirable to obtain housings for portable electronic devices that are made from polyamide compositions having excellent stiffness and impact resistance and low anisotropic warpage (i.e., good dimensional stability). By “warpage” is meant the deformation of molded parts in one or more directions that may be caused by anisotropic shrinkage of the resin during molding.
EP 0 190 001 discloses a flat glass fiber strand comprising a multiplicity of glass filaments having an oblong, elliptical, or rectangular cross-sectional shape. EP 0 196 194 discloses a strand comprising glass fibers having at least two expanded apex portions and a recess. EP 0 246 620 discloses a glass-fiber reinforced resin molded article that comprises a thermoplastic resin reinforced with glass fibers having oblong, elliptical, or cocoon-shaped cross sections. EP 0 376 616 discloses a thermoplastic resin composition reinforced with a fibrous reinforcing agent having a non-circular cross section.